Methods and Compositions for Improved Adherence of Organic Coatings to Materials

ABSTRACT

Methods and compositions for improving adhesion of an organic coating applied to a surface of a conductive substrate are provided. In aspects described, at least one reactive metal-based deposit is electrodeposited on a conductive substrate by pulse electrochemical reduction of a metal complex using a pulse scheme, wherein the metal complex is dissolved in a substantially aqueous medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/800,195, filed Feb. 1, 2019, which is herein incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under DE-FE0031659 awarded by the Department of Energy (DOE). The government has certain rights in the invention.

All references cited herein, including but not limited to, patents and patent applications are incorporated by reference in their entirety.

BACKGROUND

Metal surfaces are known to be susceptible to corrosion which can result in the degradation of the structural integrity and appearance of the underlying metal. In order to protect metal surfaces from corrosion, organic coatings (e.g., organic lining and sheeting, hot melt coatings, laminates, paints, enamels, varnishes, lacquers, dispersion coatings, emulsion coatings, powder coatings, and latex coatings) can be applied to the surface. These organic coatings use many different types of polymers (e.g., epoxies, phenolics, acrylates, latexes, urethanes and fluorinated polymers).

An organic surfaced treatment may contain many different layers comprising the organics coatings listed above, as well as inorganic coatings. Generally, the base organic layer near to the metal surface is referred to as the primer layer. The primer layer increases polarity as well as provide additional binding sites for the top organic layers to adhere. There are many types of polymer used as primer and this includes, polyetherimine (PEI); ethylene acrylic acid (EAA); but for metals epoxy-based primers are heavily used. In addition, poly(urethane) are also used for metals organic coatings as well. Epoxy organic coatings are used to coat metal surfaces and provide resistance to chemical corrosion, physical resistance to the environment, and a uniform appearance. Such epoxy coatings are often applied to, for example, on ships and chemical storage tanks. In general, epoxy resins are formed by the opening of the epoxy ring.

Pigments are used to provide color and corrosion resistance to organic coatings and include organic pigments, (e.g., azo-, phthalocyanine and anthraquinone derivatives), inorganic pigments (e.g., white titanium dioxide (titanium(IV) oxide)), iron oxides (black, yellow and red), zinc oxide and carbon black. Powdered metals (e.g., zinc and zinc phosphate) can also be used to inhibit corrosion.

However, the use of a single protective coat may not provide sufficient corrosion resistance to metal surfaces. For high performance applications. such as in the automotive and aerospace industries, a multi-stacked polymer approach can be used, with multiple pretreatments, primers top-coats and clear coats. This combination of layers can improve adhesion, wear resistance and corrosion resistance, but can also add substantial weight to the material. With interest mounting in energy efficient transportation, both the automotive and aerospace industries are actively exploring methods for incorporating lightweight materials into construction.

Methods and compositions for cathodic electrodeposition of metals via electrochemical reduction of a metal complex have been provided by an inventor herein. See, e.g., WO2017142513, WO2018222977. These applications describe, for example, water and air stable aluminum salts that can be deposited on the surface of metals (e.g., reactive metals).

What is needed are methods and compositions for increasing organic coating adhesion to material surfaces by electrodeposition resulting in reduced delamination and improved resistance to corrosion.

SUMMARY

Aspects described herein provide methods and compositions for improving adhesion of an organic coating applied to a surface of at least one conductive substrate, by electrodepositing at least one reactive metal-based deposit on a conductive substrate by pulse electrochemical reduction of a metal complex dissolved in a substantially aqueous medium, and applying an organic coating to a surface of the reactive metal-based deposit. In this aspect, less than about 1 mm scribe creep is detected up to about 250 hours after a salt spray exposure.

Further aspects provide methods and compositions for improving adhesion of an organic coating applied to a surface of at least one conductive substrate by electrodepositing at least one reactive metal-based deposit on a substrate by pulse electrochemical reduction of a metal complex dissolved in a substantially aqueous medium wherein the pulse electrochemical reduction comprises a pulse scheme comprising of a series of sequential pulses having current densities from about 5 to about 100 mA/cm², and applying an organic coating to a surface of the reactive metal-based deposit.

Yet further aspects provide methods and compositions for improving corrosion resistance of a conductive substrate by electrodepositing at least one reactive metal-based deposit on the conductive substrate by pulse electrochemical reduction of a metal complex dissolved in a substantially aqueous medium, and applying an organic coating to a surface of the reactive metal-based deposit wherein less than about 1 mm scribe creep is detected up to about 250 hours after a salt spray exposure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary comparison between the industry standard method of applying epoxy coatings to a steel surface (left panel, Industry Standard) and an example of the methods described herein (right panel, LumiShield coating);

FIGS. 2A and 2B show baseline control panels consisting of an industry standard iron phosphate treatment on steel panels (e.g., as shown in FIG. 1, left panel) with epoxy powder-coated top-coat, tested before (FIG. 2A) and after (FIG. 2B) 250 hours of salt spray exposure;

FIG. 3 shows exemplary scribe creep results following epoxy coating on LumiShield aluminum oxide tested after 250 hours of salt spray exposure use (A) Pulse 1 scheme, (B) Pulse 2 scheme, and (C) 25 mA/cm² DC for 15 minutes each;

FIGS. 4A and 4B show exemplary baseline control panels consisting of an industry standard iron phosphate treatment on steel panels with epoxy powder-coated top-coat, tested after 500 hours of salt spray exposure;

FIG. 5 shows exemplary scribe creep results following epoxy coating on LumiShield aluminum oxide tested after 500 hours of salt spray exposure use (A) Pulse 1 scheme, (B) Pulse 2 scheme, and (C) 25 mA/cm² DC for 15 minutes each;

FIGS. 6A and 6B show exemplary baseline control panels consisting of an industry standard iron phosphate treatment on steel panels with epoxy powder-coated top-coat, tested after 1000 hours of salt spray exposure;

FIG. 7 shows exemplary scribe creep results following epoxy coating on LumiShield aluminum oxide tested after 1000 hours of salt spray exposure use (A) Pulse 1 scheme, (B) Pulse 2 scheme, and (C) 25 mA/cm² DC for 15 minutes each;

FIG. 8 shows an exemplary comparison of scribed salt spray testing (ASTM D1654) of differently colored coating layers with a polyurethane topcoat with scribe adhesion testing after 1000 hours of exposure;

FIG. 9 shows exemplary morphology variations with DC current density using conditions in Table 5 and tested by visual microscopy and organic coating delamination at 1000 hours after salt spray exposure;

FIG. 10 shows exemplary morphology of coated steel panels with adhesion of ceramic loaded epoxy paint; and

FIG. 11 shows the results of an exemplary pulse electrochemical reduction using and aluminum oxide plating bath on 3″×6″ 1010 cold rolled mild steel test panels.

DETAILED DESCRIPTION

Corrosion and delamination of products made of materials such as metal or plastic limits the useful life of the product in terms of both structural integrity and appearance. When the products are used in harsh conditions (e.g., humidity, temperature, high salt content) these problems are exacerbated and could also result in hazardous conditions for the user. While coatings such as paint and pretreatments have been previously used, they do not provide satisfactory results for long term use. Reduced adhesion of organic coatings, such as paint, from the surfaces of such products leads to delamination of the organic coating from the surface and exposes the materials to adverse environmental conditions leading to corrosion and a reduced useful life for the product.

Reducing vehicle weight is an increased focus of both the aerospace and automotive industries. Thus, the ability to remove or reduce the thickness of paint layers would yield significant improvements in fuel efficiency. Methods described herein provide a direct to metal application of thinner top-coats without primer layers that reduce both weight and defect induced delamination and corrosion.

While removing paint layers could provide a significant weight savings, it is currently not possible without a loss of performance. In one aspect, an improved direct to top-coat pretreatment method that can permit removal of primer coats entirely is provided. Use of such methods can result in use of thinner painted layers without performance loss and a significant weight saving.

The thickness of organic layers is integrally linked to overcoming defects, both application defects and materials defects. Insufficient adhesion at defects from improper application, pinhole formation, or physical damage can severely limit the lifetime of paint and can lead to premature corrosion of substrates. In another aspect, a pretreatment method that increases forgiveness of these defects, where pinholes do not lead to widespread corrosion is provided. Thus, even in situations where organic coatings cannot be entirely removed, they may be reduced in thickness for cost and weight savings without generating defects that can lead to premature failure.

As shown in FIG. 1, prior methods (left panel) of coating steel utilize a phosphate pretreatment followed by an epoxy primer and a polyurethane topcoat. Industry standard treatment for painted steel utilizes physical preparation of the surface by, for example, grit blasting or a chemical treatment such as phosphating. However, as shown in FIG. 2, these methods do not provide satisfactory results after, for example, 250 hours following salt spray exposure.

Methods and composition described herein can eliminate (1) phosphate pretreatment which generates toxic waste streams and uses harsh application practices, (2) grit blasting and manual preparation of surfaces, and (3) use of primer layers. In addition, the compositions described herein can be applied directly between bare metal and top-coats.

As described herein, coating compositions described herein (referred to, for example, as the “LumiShield coating”) comprise and electroplated coating whose surface morphology, thickness and porosity may be manipulated by changing current density, pH, electrolyte concentration/identity, reactive metal identity from aluminum, magnesium, titanium, niobium, manganese, zirconium, metal concentration, metal ratio and pulse scheme.

In one aspect, the coating composition can comprise aluminum salt (e.g., 0.34M), zirconium salt (e.g., 0.1M), and NH₄Cl (e.g., 0.48M), at a pH of about 3.0 (e.g., 2.9-3.3) and used at a temperature of about 18-20 degrees C. In one aspect, the plating solution can be made from concentrates of aluminum and zirconium salt can be made by reacting of metal carbonate with a suitable acid (e.g., electron withdrawing ligands as described herein), under stirring and chilling until the desired solution concentrate in DI water is reached. In this aspect, the plating solution is synthesized from a 0.7M concentrate of aluminum salt and a 2M concentrate of zirconium salt. In this aspect, these components can be first diluted to 0.34 M and 0.1 M respectively with DI water, then an additional supporting electrolyte, ammonium chloride, is added at a concentration of 0.5M and the final pH adjusted to between 2.9 and 3.3 by the addition of hydrochloric acid. The solution can be circulated and left to equilibrate for 8 hours prior to use after which the pH can be maintained between 2.9 and 3.3.

For operation, a thermostat coil can be used with an external recirculation to maintain temperature in the bath between 18 and 20° C. for operation. A custom mixed metal oxide electrode can be used as the counter electrode and is designed to produce oxygen during the plating process. In this aspect, the steel coupon is first cleaned by an electro-cleaning process in a soap solution at 5V, followed by an acid activation step in a 20% hydrochloric acid solution and a DI rinse step prior to plating. After plating is complete the sample can be rinsed in DI water, forced air dried to remove surface water, and finally dried in a convection over at 160° C. for 2 hours. Alternate methods can be used. Such methods and compositions are described, for example, in WO2017142513 and WO2018222977, hereby incorporated by reference in their entirety.

In another aspect, the coating composition is porous in nature, with thickness and porosity controllable by variation of solution and process conditions. Controllable conditions include pH, aluminum salt concentration. Methods described herein can control, for example, current density, plating time, pulse sequence, cathode to anode ratio. In a further aspect, the coating composition has native hydroxide surface functionalization that can be detected by ATR IR (attenuated total reflectance infrared.

In another aspect, the surface hydroxides can be further functionalized by the application of silanes by a spray or dip process in a carrier solution such as alcohols or other organics.

In yet another aspect, the adhesion of polyurethane, phenolics, fluoropolymers and epoxy can be improved using the coating compositions and methods using either onto the hydroxide functionality of the applied coating composition or via a functionalized silane linkage.

The coating compositions can be used on a conductive substrate to enhance surface properties and corrosion resistance (e.g., carbon, steel, iron, nickel, conductive plastics).

Aluminum oxide coating compositions described herein can be used as a surface treatment for the attachment of silane functionality to enhance surface properties (e.g., hydrophobicity, icephobicity, corrosion resistance, abrasion resistance, adhesion to additional substrates).

The coating compositions described herein can be further impregnated with functional organic and inorganic materials such as dyes to manipulate properties such as appearance, corrosion resistance, surface lubricity.

In another aspect, the coating compositions can be used as a surface treatment for the covalent attachment of polymer top-coats including polymers from families: polyurethane (e.g. TCI 8810-9074), epoxy (e.g. Cardinal Industry Finishes E305-WH243), phenolic (e.g. Heresite P-413), fluoropolymer (e.g. Arkema Kynar and Aquatec products).

In this aspect, the surface bound polymers retain high adhesion through the LumiShield coating to the base conductive substrate with hardness and adhesion comparable to phosphate and primer technologies.

Unlike common phosphate, grit blasting or other chemical pre-treatments, exemplary coated materials described herein do not suffer delamination through scribed salt spray exposure (ASTM D1654) with adhesion and surface properties such as hydrophobicity preserved during corrosion testing.

In addition, exemplary coated samples described herein do not require additional priming from epoxy-based primers or other primers prior to top-coat application either for adhesion or corrosion resistance. In addition, exemplary coated samples described herein improve adhesion to many types of organic coatings. Commonly, organic primer layers are used for improved corrosion resistance and top-coat adhesion. In such cases, pretreatment aspects described herein can replace the need for such primers by improving direct adhesion of metal surfaces to top-coats. Through this enhanced adhesion, corrosion resistance is also improved, rendering the need for functional primers in such cases unnecessary. This pretreatment, for example, can be used to replace epoxy primers by direct application of polyurethane top-coats to the metal surface.

In one aspect, silane seal layer may be applied by standard silane application techniques such as spray coating and dip-coating using a carrier solvent such as alcohols or water and may be used with a silane content of 0.1 to 5 wt % (weight percent).

In another aspect, polymer top-coats described herein may be applied by painting, spraying, or powder coating using techniques known to the industry with no modification of the top-coating process.

Aspects described herein provide methods and compositions for improving adhesion of an organic coating applied to a surface of at least one conductive substrate, by electrodepositing at least one reactive metal-based deposit on a conductive substrate by pulse electrochemical reduction of a metal complex using a pulse scheme, wherein the metal complex is dissolved in a substantially aqueous medium, and applying an organic coating to a surface of the reactive metal-based deposit. In this aspect, less than about 1 mm scribe creep is detected up to about 250 hours after a salt spray exposure.

The term “adhesion,” as used herein, refers to the strength of association between two materials whether through chemical bonds (covalent, hydrophobic, electrostatic, etc.), magnetic or other forces. In this aspect, “adhesion” can refer to the degree to which an organic coating is associated with or bound to a substrate.

The term “conductive substrate” refers to a material that allows the flow of electric charge and is a material that is desirable to protect from adverse effects such as delamination or corrosion.

The term “electrodeposition” or “electrodepositing” refers to the deposition of metals (e.g., reactive metals) or other substances from a solvent by means of electricity on to a substrate.

The term “reactive metal-based deposit” refers to a deposit, typically an oxide, formed with a reactive metal (e.g., aluminum).

The term “pulse electrochemical reduction” refers to an electrochemical reduction reaction that occurs in a short burst or pulse of current.

The term “substantially aqueous medium” refers to a solution that comprises mostly (e.g., greater than or equal to about 50%) of an aqueous solvent (e.g., water).

The term “scribe creep” refers to the quantitative measurement in mm of the degree of removal of organic coating from a cut through the coating to the base material when exposed to corrosive conditions and removal is achieved by the scraping action of a dull blade (see, e.g., ASTM D1654).

In another aspect, the pulse scheme comprises at least one individual pulse. In another aspect, the pulse scheme comprises a plurality of pulses. The term “pulse scheme” refers to a series of one or more pulses of current. The first pulse scheme can comprise a first pulse and further comprise a plurality of pulses (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 50, 100 etc.).

In another aspect, the current density of the first pulse and the plurality of pulses can be, for example, from about 5 to about 100 mA/cm², 15 to 60 mA/cm², or 25 to 55 mA/cm².

In yet another aspect, less than 1 mm of scribe creep is detected up to about 500 hours after a salt spray exposure and less than 2 mm of scribe creep is detected up to about 1000 hours after a salt spray exposure.

In another aspect, the reactive metal-based deposit comprises a reactive metal selected from the group consisting of zirconium, aluminum, titanium, manganese, gallium, vanadium, and niobium.

In a further aspect, the organic coating is selected from one or more of epoxy, phenolic resin, polyurethane, polyester, and fluoropolymer of blends thereof.

In yet another aspect, the conductive substrate comprises a material selected from the group consisting of carbon, steel, iron, nickel, conductive plastics, and magnesium alloy.

In one aspect the metal complex comprises an electron withdrawing ligand (e.g., sulfonate ligands, sulfonamide ligands, sulfonamide ligands (e.g., bis(trifluoromethane)sulfonamide (Tf₂N)), carboxylate ligands, and β-diketonate ligands).

The sulfonate ligands can include OSO₂R¹, wherein R¹ is halo, substituted or unsubstituted C₆-C₁₈-aryl, substituted or unsubstituted C₁-C₆-alkyl, or substituted or unsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl.

The sulfonimide ligands can include N(SO₂R¹)₂, wherein R¹ is halo; substituted or unsubstituted C₆-C₁₈-aryl; substituted or unsubstituted Ci-C₆-alkyl; and substituted or unsubstituted C₆-C₁₈-aryl-Ci-C₆-alkyl.

The carboxylate ligands can include ligands of the formula R¹C(0)0-, wherein R¹ is halo; substituted or unsubstituted C₆-C₁₈-aryl; substituted or unsubstituted C₁-C₆-alkyl; and substituted or unsubstituted C₆-C₁₈-aryl-C₁-Ce-alkyl.

The electron withdrawing ligand can be selected from the group consisting of:

where R¹ is selected from the group consisting of F or CF₃.

In a further aspect, the substrate is steel, the reactive metal-based deposit comprises aluminum oxide, and the organic coating is selected from one or more of polyurethane and epoxy.

Further aspects provide methods and compositions for improving adhesion of an organic coating applied to a surface of at least one conductive substrate by electrodepositing at least one reactive metal-based deposit on a substrate by pulse electrochemical reduction of a metal complex dissolved in a substantially aqueous medium, the pulse electrochemical reduction comprising a pulse scheme having at least one pulse, wherein the at least one pulse has a current density from about 5 to about 100 mA/cm², and applying an organic coating to a surface of the reactive metal-based deposit.

Yet further aspects provide methods and compositions for improving corrosion resistance of a conductive substrate by electrodepositing at least one reactive metal-based deposit on the conductive substrate by pulse electrochemical reduction of a metal complex using a pulse scheme of a metal complex, wherein the metal complex is dissolved in a substantially aqueous medium, and applying an organic coating to a surface of the reactive metal-based deposit wherein less than about 1 mm scribe creep is detected up to about 250 hours after a salt spray exposure.

In this aspect, the pulse electrochemical reduction comprises a first pulse scheme having a first pulse comprising a current density from about 5 to about 100 mA/cm².

Further to this aspect, less than 1 mm of scribe creep is detected up to about 500 hours after a salt spray exposure and less than 2 mm of scribe creep is detected up to about 1000 hours after a salt spray exposure.

The reactive metal-based deposit can comprise a reactive metal selected from the group consisting of zirconium, aluminum, titanium, manganese, gallium, vanadium, and niobium.

The organic coating can be selected from one or more of epoxy, phenolic resin, polyurethane, polyester, and fluoropolymer of blends thereof.

The conductive substrate can comprise a material selected from the group consisting of carbon, steel, iron, nickel, and conductive plastics.

The metal complex comprises an electron withdrawing ligand.

EXAMPLES Example 1—Pulse Morphology Modification for Organic Coating Adhesion

Coating morphology can be varied by varying the current density and timing of a series of pulses in what is referred to herein as a “pulse scheme.” The adhesion of paint to a surface can be measured by both tape testing (ASTM D3359) (ASTM D3359-17, Standard Test Methods for Rating Adhesion by Tape Test, ASTM International, West Conshohocken, Pa., 2017, www.astm.org) and scribed salt spray adhesion testing (ASTM D1654)(ASTM D1654-08(2016)e1, Standard Test Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments, ASTM International, West Conshohocken, Pa., 2016, www.astm.org). The differences in adhesion can be attributed, for example, to changes in surface morphology, with color being one indication of a change in thickness and platelet structure of the surface.

A range of applied pulse schemes for aluminum oxide depositions was used, and showed variations in coating morphologies. In one example Alesta 61 Grey Epoxy powder coating was applied to a surface followed by curing at 190° C. The plates were then tested for adhesion before being scribed and exposed to ASTM B117 salt spray conditions. Samples were removed after 250 hours, 500 hours and 1000 hours without resubmission to determine the adhesive differences in the powder coat after corrosion. The samples were benchmarked against a paint adhesion standard iron phosphate pretreatment, common to the industry.

For the standard plating bath at 19° C., two different pulse schemes were tested along with an application of aluminum oxide by direct current at 25 mA/cm², for comparison. These adhesion tests were benchmarked against the industry standard paint adhesion layer—iron phosphate. The two exemplary pulse schemes were as follows:

Pulse 1 Scheme:

1. 15 mA/cm² 0.5 s

2. 20 mA/cm² 2.5 s

3. 25 mA/cm² On for 0.1 s, then Off for 0.1 s, 4 cycles.

4. 30 mA/cm² On for 0.1 s, then Off for 0.1 s, 4 cycles.

5. 35 mA/cm² On for 0.1 s, then Off for 0.1 s, 4 cycles.

6. 45 mA/cm² On for 0.1 s, then Off for 0.1 s, 4 cycles.

7. 55 mA/cm² On for 0.1 s, then Off for 0.1 s, 4 cycles.

Pulse 2 Scheme:

1. 24 mA/cm² 1 s

2. 29 mA/cm² 5 s

3. 34 mA/cm² On for 0.1 s, then Off for 0.1 s, 4 cycles.

4. 38 mA/cm² On for 0.1 s, then Off for 0.1 s, 4 cycles.

5. 43 mA/cm² On for 0.1 s, then Off for 0.1 s, 4 cycles.

6. 55 mA/cm² On for 0.1 s, then Off for 0.1 s, 4 cycles.

7. 60 mA/cm² On for 0.1 s, then Off for 0.1 s, 4 cycles.

Each of these groups was scribed per ASTM D1654 and submitted for salt spray exposure (ASTM B117). This is a standard test for determining quantitative corrosive delamination through measurement of ‘scribe creep’ the defined as the average distance away from the scribe line that organic coating can be removed from the panel by action of a dull knife. This test is common in characterization of adhesion of paints to metals, and provides data regarding corrosion resistance of the panel, as well as the ability of the pretreatment to improve adhesion of the organic coating under corrosive conditions.

FIGS. 2A and 2B show control panels consisting of an industry standard iron phosphate treatment on steel panels with epoxy powder-coated top-coat, tested before and after 250 hours of salt spray exposure. The standard coating pretreatment shown in FIGS. 2A and 2B is based on an iron phosphate substrate treated with an epoxy powder coating. The baseline control panels showed significant delamination of organic coating after only 250 hours of exposure with an average scribe creep of 2.7 mm (FIG. 2B). This level of scribe creep constitutes a test failure, and would lead to significant corrosion of the underlying steel in a real operating condition.

FIG. 3 provides the results of epoxy coating on the LumiShield aluminum oxide coating composition tested after 250 hours of salt spray exposure at (A) Pulse 1, (B) Pulse 2 and (C) 25 mA/cm² DC for 15 minutes each. As shown in FIG. 3, at 250 Hours of salt spray exposure, all aluminum oxide coated panels show less than 1 mm of scribe creep or paint delamination.

TABLE 1 Summary of scribe creep results from plates in FIG. 3 for (A) Pulse 1, (B) Pulse 2, and (C) DC and control plates measured after 250 hours of salt spray exposure (ASTM B117) and tested via methods in ASTM D1654. 250 Hours (ASTM B117) Pulse 1 1 2 2 DC DC Control Control Average Creep/mm 0.00 0.00 0.00 0.00 0.00 0.00 2.54 2.85

FIGS. 4A and 4B show control panels consisting of an industry standard iron phosphate treatment on steel panels with epoxy powder-coated top-coat, tested before and after 500 hours of salt spray exposure. After 500 hours of salt spray exposure plates were again tested for delamination and corrosive attack. Control panels now show even more scribe creep delamination as corrosion can further spread and damage the plates.

FIG. 5 provides the results of epoxy coating on the LumiShield aluminum oxide coating composition tested after 500 hours of salt spray exposure at (A) Pulse 1, (B) Pulse 2 and (C) 25 mA/cm² DC for 15 minutes each. As shown in FIG. 5, at 500 hours the aluminum oxide coated plates show some differences in adhesive performance. Plates coated by Pulse 1 show almost no delamination detected at 250 and 500 hours of exposure. Pulse 2 starts to show some isolated sites of delamination particularly around the intersection point of the X-scribe. The DC coated panels now show the beginnings of the delamination at the x-scribe. None of the tests at 500 hours of salt spray exposure constitute a coating failure for ASTM D1654 using the LumiShield coating.

TABLE 2 Summary of scribe creep results from plates in FIG. 5 for (A) Pulse 1, (B) Pulse 2, and (C) and control plates measured after 500 hours of salt spray exposure (ASTM B117) and tested via methods in ASTM D1654. 500 Hours (ASTM B117) Pulse 1 1 2 2 DC DC Control Control Average Creep/mm 0.16 0.12 0.20 0.78 0.70 0.32 5.08 4.62

FIGS. 6A and 6B show control panels consisting of an industry standard iron phosphate treatment on steel panels with epoxy powder-coated top-coat, tested before and after 1000 hours of salt spray exposure. After 1000 hours of salt spray exposure, significant corrosion and delamination is found in the control panels.

FIG. 7 provides the results of epoxy coating on the LumiShield aluminum oxide coating composition tested after 500 hours of salt spray exposure at (A) Pulse 1, (B) Pulse 2 and (C) 25 mA/cm² DC for 15 minutes each. As shown in FIG. 7, the LumiShield aluminum oxide coating showed significant improvement compared to the control panels (see Table 4 below).

TABLE 3 Summary of scribe creep results from plates in 7 for Pulse 1, Pulse 2, DC and control plates measured after 1000 hours of salt spray exposure (ASTM B117) and tested via methods in ASTM D1654. 1000 Hours (ASTM B117) Pulse 1 1 2 2 DC DC Control Control Average Creep/mm 1.77 1.72 4.54 2.81 1.54 3.47 7.81 8.93

In order to quantify the improvement in organic coating adhesion by using the aluminum oxide coatings, Table 4 compares the percentage of improvement in each case versus the industry standard coating. In the case of Pulse 1 coated panels, a 97% improvement after 500 hours in performance is found for the LumiShield coated panels compared to control panels, and shows the biggest improvement.

TABLE 4 Summary data for each plating condition compared with the industry standard control plates. Pulse 1 Pulse 2 DC Control Average Creep 250 Hours 0.00 0.00 0.00 2.69 Average Creep 500 Hours 0.14 0.49 0.51 4.85 Average Creep 1000 Hours 1.75 3.68 2.51 8.37

As shown in Table 4, treatment with the LumiShield aluminum oxide coating using the Pulse 1 scheme, Pulse 2 scheme, and DC scheme improved scribe creep by up to 80% at 1000 hours.

Example 2—Coating Color Modification with Time for Organic Coating Adhesion

As the aluminum oxide coating grows, it goes through multiple phases, each with a characteristic color attributed to refractive changes in the growth morphology. The color is indicative of the changing morphology and thickness. By stopping layer growth at discrete time increments, these colors can be isolated and tested for relative adherence to organic coating.

For each test the Pulse 1 plating conditions from Example 1 were used in the same standard aluminum oxide plating bath. The test panels are 3″×6″ 1010 cold rolled mild steel and are shown in FIG. 11.

The coatings were dried for 2 hours at 160° C. For each sample, a polyurethane powder coated paint was applied (Akzo Nobel, Interpon 200) and tested by tape adhesion testing (ASTM D3359) and scribed salt spray testing (ASTM D1654). The results for these are shown in FIG. 8. FIG. 8 shows the results of scribed salt spray testing (ASTM D1654) of each coating layer with a polyurethane topcoat with scribe adhesion testing after 1000 hours of exposure.

These results show that iron phosphate controls provides no corrosion resistance and no adhesion of polyurethane to steel. In contrast, the LumiShield aluminum oxide coating and pulse methods, as disclosed herein, shows an improvement over iron phosphate. In one aspect, the coating time can further improve adhesion. Thicker, white coatings with more granular structure are shown to give improved adhesion of polyurethane to steel.

Example 3—Morphology vs. Adhesion Through Current Density Changes

A study of morphology variation with application of DC current at three different current densities was conducted. The applied conditions are given in the following table.

TABLE 5 Current Density/ Time/ mA/cm² mins Post-treatment A 16 30 None B 16 30 (3-Isocyanatopropyl)triethoxysilane C 18 30 None D 18 30 (3-Isocyanatopropyl)triethoxysilane E 20 30 None F 20 30 (3-Isocyanatopropyl)triethoxysilane

FIG. 9 shows morphology variations with DC current density using conditions in Table 5 and tested by visual microscopy and paint delamination at 1000 hours of salt spray exposure.

With different applied DC currents, variations in morphology of deposited aluminum oxide could be visualized. These changes in morphology are tied to coating thickness and are shown by variations in color of the coating. The color changes are apparent with the naked eye, and confirmed by visual microscopy at 1000× under coaxial light (FIG. 9). As current density increases, and deposition thickness increases, the color changes from a grey/blue (A and B) to a gold (C and D) and finally to a white appearance (E and F). The different coating morphologies were then tested by applying a standard polyurethane top-coat and tested for paint adhesion under corrosion by using a scribed salt spray test (ASTM D1654).

In some cases (B, D and F) a binder layer of (3-Isocyanatopropyl)triethoxysilane was sprayed as a post-treatment to facilitate polyurethane adhesion. It is shown from these tests that the fully blue/gold coated sample shows improved adhesion of polyurethane over both blue/grey and fully white coated steel plates. This is the case both with and without the silane binder layer.

Example 4—Adhesion of Ceramic Loaded Epoxy Paint to Mild Steel Coupons

TABLE 6 Current Density/ Step # Timing/s mA/cm² 1 0.8 20 2 0.1 0 3 0.2 25 4 0.2 0 5 0.2 25 6 0.2 0 7 0.2 40 8 0.2 0 9 0.2 40 10 0.2 0 11 0.2 55 12 0.2 0 13 0.2 55 14 0.2 0 15 0.2 70 16 0.2 0 17 0.2 70 18 0.2 0

FIG. 10 shows plates coated with aluminum oxide pretreatment both with and without epoxy silane post-treatment. For plates A and B, no post-treatment was used other than drying. For plates C and D, an epoxy silane was sprayed onto the coating to enhance adhesion to the epoxy paint as a post-treatment. All six plates were compared in adhesion by using the cross-hatch adhesion method (ASTM D3359). ASTM D3359-17, Standard Test Methods for Rating Adhesion by Tape Test, ASTM International, West Conshohocken, Pa., 2017, www.astm.org) and scribed salt spray adhesion testing.

While the aspects described herein have been disclosed with reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof. 

What is claimed is:
 1. A method of improving adhesion of an organic coating applied to a surface of at least one conductive substrate, comprising: electrodepositing at least one reactive metal-based deposit on a conductive substrate by pulse electrochemical reduction of a metal complex using a pulse scheme, wherein the metal complex is dissolved in a substantially aqueous medium; and applying an organic coating to a surface of the reactive metal-based deposit wherein less than about 1 mm scribe creep is detected up to about 250 hours after a salt spray exposure.
 2. The method of claim 1, wherein the pulse scheme comprises at least one individual pulse.
 3. The method of claim 2, wherein the pulse scheme further comprises a plurality of pulses.
 4. The method of claim 3, wherein a current density of the at least one individual pulse and the plurality of pulses is from about 5 to about 100 mA/cm².
 5. The method of claim 4, wherein the current density of the at least one individual pulse and the plurality of pulses is from about 15 to 60 mA/cm².
 6. The method of claim 5, wherein the current density of the at least one individual pulse and the plurality of pulses is from about 25 to 55 mA/cm².
 7. The method of claim 1, wherein less than 1 mm of scribe creep is detected up to about 500 hours after a salt spray exposure.
 8. The method of claim 1, wherein less than 2 mm of scribe creep is detected up to about 1000 hours after a salt spray exposure.
 9. The method of claim 1, wherein the reactive metal-based deposit comprises a reactive metal selected from the group consisting of zirconium, aluminum, titanium, manganese, gallium, vanadium, and niobium.
 10. The method of claim 9, wherein the reactive metal is aluminum.
 11. The method of claim 1, wherein the organic coating is selected from one or more of epoxy, phenolic resin, polyurethane, polyester, and fluoropolymer of blends thereof.
 12. The method of claim 1, wherein the conductive substrate comprises a material selected from the group consisting of carbon, steel, iron, nickel, and conductive plastics.
 13. The method of claim 12, wherein the substrate comprises steel.
 14. The method of claim 1, wherein the metal complex comprises an electron withdrawing ligand.
 15. The method of claim 14, wherein the electron withdrawing ligand is selected from the group consisting of sulfonate ligands, sulfonimide ligands, sulfonamide ligands, carboxylate ligands; and β-diketonate ligands.
 16. The method of claim 15, wherein the sulfonate ligands comprise OSO₂R¹, wherein R¹ is halo, substituted or unsubstituted C₆-C₁₈-aryl, substituted or unsubstituted C₁-C₆-alkyl, or substituted or unsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl.
 17. The method of claim 15, wherein the sulfonimide ligands comprise N(SO₂R¹)₂, wherein R¹ is wherein R¹ is halo; substituted or unsubstituted C₆-C₁₈-aryl; substituted or unsubstituted Ci-C₆-alkyl; and substituted or unsubstituted C₆-C₁₈-aryl-C₁-C₆-alkyl.
 18. The method of claim 15, wherein the carboxylate ligands include ligands of a formula R¹C(0)0-, wherein R¹ is wherein R¹ is halo; substituted or unsubstituted C₆-C₁₈-aryl; substituted or unsubstituted C₁-C₆-alkyl; and substituted or unsubstituted C₆-C₁₈-aryl-C₁-Ce-alkyl.
 19. The method of claim 14, wherein the electron withdrawing ligand is selected from the group consisting of:

where R¹ is selected from the group consisting of F or CF₃.
 20. The method of claim 1, wherein the substrate is steel, the reactive metal-based deposit comprises aluminum oxide, and the organic coating is selected from one or more of polyurethane and epoxy.
 21. A method of improving adhesion of an organic coating applied to a surface of at least one conductive substrate, comprising: electrodepositing at least one reactive metal-based deposit on a substrate by pulse electrochemical reduction of a metal complex dissolved in a substantially aqueous medium, the pulse electrochemical reduction comprising a pulse scheme having at least one pulse, wherein the at least one pulse has a current density from about 5 to about 100 mA/cm²; and applying an organic coating to a surface of the reactive metal-based deposit.
 22. The method of claim 21, wherein the pulse scheme further comprises a plurality of pulses.
 23. A method of improving corrosion resistance of a conductive substrate, comprising: electrodepositing at least one reactive metal-based deposit on the conductive substrate by pulse electrochemical reduction of a metal complex using a pulse scheme, wherein the metal complex is dissolved in a substantially aqueous medium; and applying an organic coating to a surface of the reactive metal-based deposit wherein less than about 1 mm scribe creep is detected up to about 250 hours after a salt spray exposure.
 24. The method of claim 23, wherein the pulse scheme comprises at least one individual pulse having a current density from about 5 to about 100 mA/cm².
 25. The method of claim 23, wherein less than 1 mm of scribe creep is detected up to about 500 hours after a salt spray exposure.
 26. The method of claim 23, wherein less than 2 mm of scribe creep is detected up to about 1000 hours after a salt spray exposure.
 27. The method of claim 23, wherein the reactive metal-based deposit comprises a reactive metal selected from the group consisting of zirconium, aluminum, titanium, manganese, gallium, vanadium, and niobium.
 28. The method of claim 27, wherein the reactive metal is aluminum.
 29. The method of claim 23, wherein the organic coating is selected from one or more of epoxy, phenolic resin, polyurethane, polyester, and fluoropolymer of blends thereof.
 30. The method of claim 23, wherein the conductive substrate comprises a material selected from the group consisting of carbon, steel, iron, nickel, conductive plastics.
 31. The method of claim 30, wherein the substrate comprises steel.
 32. The method of claim 23, wherein the metal complex comprises an electron withdrawing ligand. 